2486. Append Characters to String to Make Subsequence

Medium

You are given two strings s and t consisting of only lowercase English letters.

Return the minimum number of characters that need to be appended to the end of s so that t becomes a subsequence of s.

A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.

Example 1:

• Input: s = "coaching", t = "coding"
• Output: 4
• Explanation: Append the characters "ding" to the end of s so that s = "coachingding".\ Now, t is a subsequence of s ("coaching*ding*").\ It can be shown that appending any 3 characters to the end of s will never make t a subsequence.

Example 2:

• Input: s = "abcde", t = "a"
• Output: 0
• Explanation: t is already a subsequence of s ("abcde").

Example 3:

• Input: s = "z", t = "abcde"
• Output: 5
• Explanation: Append the characters "abcde" to the end of s so that s = "zabcde".\ Now, t is a subsequence of s ("z*abcde*").\ It can be shown that appending any 4 characters to the end of s will never make t a subsequence.

Constraints:

• 1 <= s.length, t.length <= 105
• s and t consist only of lowercase English letters.

Solution:

class Solution {

    /**
     * @param String $s
     * @param String $t
     * @return Integer
     */
    function appendCharacters($s, $t) {
        $i = 0;

        foreach(str_split($s) as $c) {
            if ($c == $t[$i]) {
                if (++$i == strlen($t)) {
                    return 0;
                }
            }
        }

        return strlen($t) - $i;
    }
}

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